The main reason is that even though Turkish Airlines offers a really solid product, their customer service and dealing with IRROPS is a 1-star service, so the average of 5 and 1 would be 3. They deserved it with cost-cutting of the meals, not opening the AC until the aircraft has pushed back, the fact that some of their staff that can't speak clear English ( I remember being asked by the cabin crew to translate what the passenger next to me was asking ). Also, their lounge product and business class meals are the same for more than 10 years. If they have decided to participate back in SkyTrax ratings, maybe with their new 787-9 and A350 product they could shift back to 4-star as they have seemed that they've understood their marketing faults these days. I remember the days, back in 2017, where TK had paid for advertisement boards all around Istanbul to show that they are the best European Airline awarded by SkyTrax for 7 consecutive years.